s390/qeth: fix overestimated count of buffer elements

qeth_get_elements_for_range() doesn't know how to handle a 0-length
range (ie. start == end), and returns 1 when it should return 0.
Such ranges occur on TSO skbs, where the L2/L3/L4 headers (and thus all
of the skb's linear data) are skipped when mapping the skb into regular
buffer elements.

This overestimation may cause several performance-related issues:
1. sub-optimal IO buffer selection, where the next buffer gets selected
   even though the skb would actually still fit into the current buffer.
2. forced linearization, if the element count for a non-linear skb
   exceeds QETH_MAX_BUFFER_ELEMENTS.

Rather than modifying qeth_get_elements_for_range() and adding overhead
to every caller, fix up those callers that are in risk of passing a
0-length range.

Fixes: 2863c61334aa ("qeth: refactor calculation of SBALE count")
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index ca72f3311004a3d020ed07266596ff63ce740b26..30457fca30c57066cce0f014941532b4a9867d61 100644 (file)
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -3898,10 +3898,12 @@ EXPORT_SYMBOL_GPL(qeth_get_elements_for_frags);
 int qeth_get_elements_no(struct qeth_card *card,
                     struct sk_buff *skb, int extra_elems, int data_offset)
 {
-       int elements = qeth_get_elements_for_range(
-                               (addr_t)skb->data + data_offset,
-                               (addr_t)skb->data + skb_headlen(skb)) +
-                       qeth_get_elements_for_frags(skb);
+       addr_t end = (addr_t)skb->data + skb_headlen(skb);
+       int elements = qeth_get_elements_for_frags(skb);
+       addr_t start = (addr_t)skb->data + data_offset;
+
+       if (start != end)
+               elements += qeth_get_elements_for_range(start, end);
 
        if ((elements + extra_elems) > QETH_MAX_BUFFER_ELEMENTS(card)) {
                QETH_DBF_MESSAGE(2, "Invalid size of IP packet "

diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c
index b0c888e86cd4a0980ff42e49f06d6022c93f4de7..3421893c37a49dc450554fbf57650deeb3c8adec 100644 (file)
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2450,11 +2450,12 @@ static void qeth_tso_fill_header(struct qeth_card *card,
 static int qeth_l3_get_elements_no_tso(struct qeth_card *card,
                        struct sk_buff *skb, int extra_elems)
 {
-       addr_t tcpdptr = (addr_t)tcp_hdr(skb) + tcp_hdrlen(skb);
-       int elements = qeth_get_elements_for_range(
-                               tcpdptr,
-                               (addr_t)skb->data + skb_headlen(skb)) +
-                               qeth_get_elements_for_frags(skb);
+       addr_t start = (addr_t)tcp_hdr(skb) + tcp_hdrlen(skb);
+       addr_t end = (addr_t)skb->data + skb_headlen(skb);
+       int elements = qeth_get_elements_for_frags(skb);
+
+       if (start != end)
+               elements += qeth_get_elements_for_range(start, end);
 
        if ((elements + extra_elems) > QETH_MAX_BUFFER_ELEMENTS(card)) {
                QETH_DBF_MESSAGE(2,